1. Field of the Invention
This invention relates to an image forming apparatus using the electrophotographic method, and particularly to an image forming apparatus such as a copier, a printer or a facsimile apparatus.
2. Related Background Art
Heretofore, in an image forming apparatus capable of polychromatic printing such as a color printer or a color copier, the positions of a plurality of detachably mountable process cartridges having photosensitive drums, etc., and an optical unit having an optical system for applying light conforming to image information to each photosensitive drum have been determined by front and rear side plates forming the frame of the main body of the apparatus.
Of these side plates, the rear side plate is provided with a driving portion for driving the process cartridges, and a portion of the front side plate is provided with an opening portion for effecting the interchange of the process cartridges. By this opening portion of the front side plate provided to interchange the process cartridges, a holding portion in one region of a process cartridge, when the process cartridge is inserted, is lost, but the design is made such that the process cartridge can be held by a holding plate or the like discrete from this side plate.
This holding plate is provided for each of the plurality of process cartridges, and each holding plate has incorporated therein an adjusting mechanism or the like for holding the shaft of the photosensitive drum of the process cartridge at a predetermined position.
The optical units corresponding to these adjusting mechanisms of the holding plates are incorporated by throwing in, and for these optical units, many means for effecting the adjustment of the process cartridges have been proposed.
Also, in a case where a plurality of process cartridges are held by a holding plate, there is incorporated a mechanism for holding the process cartridges at a predetermined position in vertical and horizontal directions with the shaft the photosensitive drum as the reference.
In the above-described construction according to the prior art, in order to form a color image, an adjusting mechanism for the plurality of process cartridges is necessary, and a mechanism for adjusting each of the process cartridges of black (hereinafter abbreviated as K), yellow (hereinafter abbreviated as Y), magenta (hereinafter abbreviated as M) and cyan (hereinafter abbreviated as C) is incorporated and constructed.
These process cartridges, when inserted and mounted from the aforedescribed opening portion of the front side plate, are mounted with the driving portion of the fixed rear side plate as the reference, and further the position of each process cartridge is adapted to be regulated by a holding plate provided near the opening portion of the front side plate.
In the above-described construction according to the conventional art, however, the holding plate and the driving portion of the rear side plate exhibit positional deviation due to the accumulation of the tolerances of parts and therefore, as a matter of course, the positions of adjacent ones of the process cartridges are irregular within the range of the tolerance and further, when an optical system for applying light (image light) to the photosensitive drums is mounted, the irradiated positions on the photosensitive drums exhibit positional deviation.
Also, in order to correct the positional deviation of these process cartridges and the optical system, various correcting mechanisms and adjusting mechanisms are incorporated on the holding plate, and particularly if an attempt is made to raise a process cartridge when the longitudinal positional relation between the optical unit and the process cartridge is to be adjusted, the holding mechanism receives the weight of the process cartridge, and if an attempt is made to raise the plurality of process cartridges at one time, the load applied to the holding mechanism becomes great, and operability has sometimes become poor.
It is an object of the present invention to provide an image forming apparatus which enables the regulation of the position of an image bearing member unit to be accomplished easily, that is, which improves usability.
It is another object of the present invention to provide an image forming apparatus in which the load when a supporting member is moved can be mitigated.
Further objects of the present invention will become apparent by reading the following detailed description.